Debris Disks, Small Bodies, and Planets Alexander V. Krivov Astrophysical Institute and University Observatory Friedrich Schiller University Jena 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Components of a “mature” planetary system 1. Debris disks stem from small bodies 2. Debris disks are sculptured by planets – directly and via small bodies 3. Debris disks are easier to observe than planets and small bodies => important! Planetesimals Planets Debris disk Star Circumstellar material 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Outline ● New observations ● Debris disks themselves ● Debris disks and small bodies ● Debris disks, small bodies and planets ● Summary 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

New Observations

Vega “The Big Four“ (  Lyr,  Pic,  Eri,  PsA) revisited Holland et al., Nature 392, 788 (1998) Su et al., ApJ 628, 427 (2005) Spitzer / MIPS: huge (1000AU) featureless disk seen pole-on 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

 Eridani “The Big Four“ (  Lyr,  Pic,  Eri,  PsA) revisited Greaves et al., ApJ 619, L187 (2005) JCMT / SCUBA five years after discovery: signs of rotation, at least three features real Greaves et al., ApJ 506, L133 (1998) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

 Pic “The Big Four“ (  Lyr,  Pic,  Eri,  PsA) revisited 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Galland et al., AAp 447, 355 (2006) New radial velocity constraints on presumed planets: no Jupiter inside 1AU Wahhaj et al. (2003) Weinberger et al. (2003) Telesco et al. (2005) New images of the inner disk (<100AU)

AU Mic New disks resolved (vis, IR, sub-mm) Kalas et al. Science 303, 1990 (2004) Liu, Science 305, 1442 (2004) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 M1Ve 0.5 M sun 0.1 L sun ~20 Myr 9.9 pc vis and NIR, 88” U. Hawaii and Keck Coeval with  Pic, but an M-type star

HD Greaves et al., MNRAS 351, L54 (2004) Schneider et al., ApJ 629, L117 (2005) Kalas, ApJ, 633, L169 (2005)  Cet New disks resolved (vis, IR, sub-mm) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 A0 30 Myr? 110 pc vis and NIR, NICMOS and 88” U. Hawaii G8V, ~10 Gyr, 3.7 pc sub-mm, JCMT / SCUBA Older than the Sun!

More than 300 disks in total Meyer et al., ApJS 154, 422 (2004) Many more unresolved disks (IR excesses) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Greaves, Science 307, 68 (2005) Statistics: age dependence Protoplanetary disks Transitional disks Debris disks  Large drop after 10Myr  No change after 400Myr, a linear decay instead  (cf. Habing et al., Nature 401, 456,1999)  No obvious dependence on central star's properties 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Statistics: stars with disks vs stars with planets...but (almost) no stars with RV planets have debris disks Greaves et al., MNRAS 348, 1097 (2004) Nearly all stars with debris disks have distant planets Saffe & Gomes (2004) and Beichman et al (2005) came to different conclusions. The question remains open... 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Debris Disks Themselves

Birth, life, and death of dust grains 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Dust sources: ● planetesimals (collisions) ● comets (activity) ● grain-grain collisions Dust sinks: ● sublimation ● collisions and RP blowout ● ejection by planets Dust evolution: ● Stellar gravity ● Direct radiation pressure ● Poynting-Robertson drag ● Grain-grain collisions ● Gas drag ● Gravity of planets ● Lorentz force Birth, life, and death of dust grains 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Direct radiation pressure only “reduces” the mass of the star, dust grain orbits remain Keplerian Stellar gravity + radiation pressure 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Talks by Gerhard Wurm & Oliver Krauss

Stellar gravity + radiation pressure ●  -meteoroids (in bound, elliptic orbits) ● two types of  -meteoroids (in unbound, hyperbolic orbits) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Stellar gravity + radiation pressure A typical boundary between  - and  -meteoroids: 1-10  m 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

● Orbits of  -meteoroids shrink and circularize ● The grains eventually sublimate near the star Wyatt & Whipple, ApJ 111, 134 (1950) Breiter & Jackson, MNRAS 299, 237 (1998) Poynting-Robertson drag 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Collisions Collisional grinding: pebbles... sand... fine dust... Rates Min relative velocity for fragmentation:~100m/s Random velocities in a disk:~1km/s => collisions are disruptive Largest fragment's mass / collider's mass (assuming 1km/s relative velocity):~10 -3 => pounding is efficient Outcomes Collisional time ~ orbital period 10 optical depth ~ orbital periods => collisions are frequent 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Poynting-Robertson drag vs collisions Zodiacal cloud  Pictoris Krivov, Mann & Krivova, AAp 362, 1127 (2000)Leinert & Grün, In Phys.of Inner Heliosphere (1990) Except in old dilute disks, P-R drag plays a minor role! 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Contradictory observations of  Pic and AU Mic (12Myr): much gas (gas:dust ~ 100:1) Thi et al. (2001), Brandeker et al. (2004),... little gas (gas:dust < 6:1) Lecavelier et al. (2001), Roberge et al. (2005),... Dynamical arguments: very little gas (gas:dust < 1:1) Thebault & Augereau, AAp 437, 141 (2005) Consequences: gas planets must already have formed there, and there is evidence for that (e.g., Mouillet et al. 1997, Liu 2004) Gas drag 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Talk by Inga Kamp

Size distribution (the Vega disk example) Dohnanyi's (1969) power law (alpha-meteoroids only) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Torsten Löhne

beta-meteoroids Size distribution (the Vega disk example) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Torsten Löhne

...timescales depend on distance... Size distribution (the Vega disk example) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Torsten Löhne

Size distribution (the Vega disk example) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Torsten Löhne

Dominant size, waviness, presence of  -meteoroids The steady state distribution Size distribution (the Vega disk example) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Krivov, Löhne & Sremcevic, AAp (submitted) There is an upper limit on the radial slope Radial distribution (the Vega disk example) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 The steady state distribution

Debris Disks and Small Bodies

Short-term evolution of debris disk Supercollision Dust clump Longitudinal spread and formation of a dust ring Radial spread outward in ~0.1-1 Myr Non-steady-state: e.g. due to recent major collisions (Wyatt & Dent, MNRAS 334, 589, 2002; Kenyon & Bromley, AJ 130, 269, 2005) Krivov, Löhne & Sremcevic, AAp (submitted) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Torsten Löhne

Long-term evolution of debris disk Collisional depletion of parent bodies (Dominik & Decin, ApJ 598, 626, 2003) EKB Krivov, Sremcevic & Spahn, Icarus 174, 105, (2005) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Long-term evolution of debris disk A nearly 1/ t decay of parent body populations should cause gradual depletion of debris disks over Gyr-scales Collisional depletion of parent bodies (Dominik & Decin, ApJ 598, 626, 2003) Krivov, Löhne & Sremcevic, AAp (submitted) EKB Krivov, Sremcevic & Spahn, Icarus (2005) Vega disk 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Debris Disks, Small Bodies, and Planets

Global structure – asymmetries and warps Observed in several resolved disks 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

warp is spreading outwards (Mouillet et al., AAp (1997 ) : R warp =R warp (M star, M planet, a planet, time) Offset (e,  Warp (i,  Global structure – asymmetries and warps Suggested explanation: secular perturbations from an embedded planet (alternatively, asymmetry can stem from the disk-ISM interaction) Artymowicz & Clampin, ApJ (1997) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Radial substructure - inner gaps Seen in resolved disks Inferred from SEDs Moro-Martin, Wolf & Malhotra, ApJ 621, 1079 (2005) Curves: w/o planets, grey bands: with planets Inner gaps with radii of a few to a few tens of AU are found to be typical Greaves et al., ApJ 506, L133 (1998) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Talk by Sebastian Wolf

Both scenarios look plausible, both require a planet to confine the planetesimal belt Radial substructure - inner gaps Scenario I: ● Dust production in a planetesimal belt ● P-R drift of dust inward to planet orbit ● Planet acts as a dynamical barrier Scenario II (simpler, robuster!) ● Dust production in a planetesimal belt ● Subsequent collisional cascade ● RP spreads dust outward from the belt 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Spatially-resolved spectrophotometry: evidence for several rings of fine dust Okamoto et al., Nature 431, 660 (2004) Radial substructure - rings Wahhaj et al. (2003) Weinberger et al. (2003) Telesco et al. (2005) Images: evidence for several rings of large dust Observed in several resolved disks 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Florian Freistetter

Both scenarios look plausible Radial substructure - rings Scenario I: ● Dust production “somewhere” outside ● P-R drift of dust inward to resonances ● Ring formation almost at planet orbit Scenario II (simpler, robuster!) ● Dust production in a planetesimal belt ● Therefore, higher dust density there ● Ring appears at the belt location Dermott et al, Nature 369, 719 (1994) A simple kinetic model: localized dust production, P-R drag and collisions Wyatt, AAp 433, 1007 (2005) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Liou et al. (2000): ~1M J, a p =40AU, e p =0.01 Ozernoy et al. (2000): 0.2M J, a p =55-65AU, e p =0 Quillen & Thorndike (2002): 0.1M J, a p =42AU, e p =0.3 Deller & Maddison (2005): the same + 2nd AU  Eridani Azimuthal substructure - clumps Greaves et al., ApJ 506, L133 (1998) Quillen & Thorndike, ApJ 578, L149 (2002) Observations Models 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Martina Queck

Edgeworth-Kuiper belt Azimuthal substructure - clumps Observations Models...none... Liou & Zook, AJ 118, 580 (1999) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Theory (trapping efficiency, timescales etc) (Beauge, Ferraz-Mello, Jackson, Lazzaro, Liou, Roques, Scholl, Sicardy, Weidenschilling,... (1990s) Star Planet Voids Clumps Inner gap Standard scenario: P-R drift & trapping in exterior MMRs Azimuthal substructure - clumps 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Difficulties with this scenario Azimuthal substructure - clumps P-R timescale and timescale of resonant eccentricity pumping >> timescale of collisional destruction ! 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Azimuthal substructure - clumps Works only in disks with  > ! Krivov, Queck & Sremcevic, in prep. Standard scenario: ● Dust production in a planetesimal belt ● P-R drift of dust inward to resonances ● Capture and formation of clumps Wyatt, ApJ 598, 1321 (2003) Alternative scenario: ● Dust production in a family of resonant planetesimals ● Dust remains in the same resonance Works always (but requires~0.1-1 M earth in planetesimals) 4th Planet Formation Workshop Heidelberg, 1-3 March 2006 Poster by Martina Queck

Summary

Debris disks are: a natural component of planetary systems at later evolutionary stages, and therefore important objects to study; maintained by, and deliver information on, small body populations; indicators of planets; 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Studies of debris disks complete the census of planetary systems and can certainly contribute to answering the great question: “How do the planetary systems form and evolve?” 4th Planet Formation Workshop Heidelberg, 1-3 March 2006

Many thanks to my collaborators Torsten Löhne (poster!) Martina Queck (poster!) Florian Freistetter (poster!)